The modular group $\mathrm{PSL}_2(\mathbb{Z})$ has 3 generators $A,B,C$, where $$A:z\to z+1,\quad B:z\to z-1,\quad C:z\to -1/z.$$
I want to compute the automaton that recognize the words of the modular group, where the input symbols are just $\{A,B,C\}$. But the above representation is not in the standard form of a coxeter group system.
My problem is: how can one do the computation in this case? Or are there any programs that do the work available?